Lead sulfide quantum dot-based nanostructured solar cells

The use of PbS quantum dots (QDs) acting as light absorbers in a range of nanostructured solar cell devices has been investigated. The impact of different QD deposition methods, of the nature and structure of different metal oxides serving as electrodes, as well as interface and surface effects on device performance has been explored. Chapter 3 describes the application of in situ grown PbS QDs as absorber layer for extremely thin absorber solar cells with the inorganic solid hole transporter CuSCN. A polystyrene-block-poly(ethylene oxide) block copolymer was employed as a structure-directing agent for the synthesis of mesoporous TiO2 metal oxide thin films with high surface area and ordered porous structure. Chapter 4 outlines further work in which water-solubilized ex situ grown QDs capped with L-glutathione ligands were employed in order to improve the loading of the PbS QDs onto the internal surface of the porous oxide. Successful sensitization was achieved by inducing opposite surface charges on the surfaces of the QDs and the oxide in order to attract and attach QDs onto the surface of the porous supporting oxide film. The sensitized TiO2 electrodes were used to make efficient liquid electrolyte quantum-dot-sensitized solar cells (QDSCs). Chapter 5 describes the use of SnO2, which has a lower lying conduction band than TiO2, to fabricate scaffolding electrodes that were sensitized with water-solubilized PbS QDs. Passivation of the SnO2 electrodes with a thin layer of MgO, TiO2 and a combination of both was utilized to investigate the effect of surface treatments on the performance of solid-state QDSCs, using Spiro-OMeTAD as organic hole transporter. Chapters 6 and 7 deal with different approaches towards interface tuning in solid-state QDSCs. This part of the work involved the study of solar cell devices utilizing in situ grown PbS QDs with and without organic and inorganic surface passivation, and ex situ grown PbS QDs anchored on mesoporous TiO2 via organic linker molecules. The performance of the fabricated solar cells was evaluated with standard current-voltage and incident-photon-to-collected-electron efficiency measurements, and physical parameters of the devices were characterised with frequency- and time-resolved techniques such as electrochemical impedance spectroscopy, intensity-modulated photovoltage/photocurrent spectroscopy, and open circuit voltage decay measurements, respectively. Overall, the work highlights the importance of surface passivation of QDs, loading of the QDs onto porous semiconducting oxide electrodes, as well as the significance of interfacial effects between QDs, oxides and hole transporter to achieve high-efficiency devices

Lead sulfide quantum dot-based nanostructured solar cells

The use of PbS quantum dots (QDs) acting as light absorbers in a range of nanostructured solar cell devices has been investigated. The impact of different QD deposition methods, of the nature and structure of different metal oxides serving as electrodes, as well as interface and surface effects on device performance has been explored. Chapter 3 describes the application of in situ grown PbS QDs as absorber layer for extremely thin absorber solar cells with the inorganic solid hole transporter CuSCN. A polystyrene-block-poly(ethylene oxide) block copolymer was employed as a structure-directing agent for the synthesis of mesoporous TiO2 metal oxide thin films with high surface area and ordered porous structure. Chapter 4 outlines further work in which water-solubilized ex situ grown QDs capped with L-glutathione ligands were employed in order to improve the loading of the PbS QDs onto the internal surface of the porous oxide. Successful sensitization was achieved by inducing opposite surface charges on the surfaces of the QDs and the oxide in order to attract and attach QDs onto the surface of the porous supporting oxide film. The sensitized TiO2 electrodes were used to make efficient liquid electrolyte quantum-dot-sensitized solar cells (QDSCs). Chapter 5 describes the use of SnO2, which has a lower lying conduction band than TiO2, to fabricate scaffolding electrodes that were sensitized with water-solubilized PbS QDs. Passivation of the SnO2 electrodes with a thin layer of MgO, TiO2 and a combination of both was utilized to investigate the effect of surface treatments on the performance of solid-state QDSCs, using Spiro-OMeTAD as organic hole transporter. Chapters 6 and 7 deal with different approaches towards interface tuning in solid-state QDSCs. This part of the work involved the study of solar cell devices utilizing in situ grown PbS QDs with and without organic and inorganic surface passivation, and ex situ grown PbS QDs anchored on mesoporous TiO2 via organic linker molecules. The performance of the fabricated solar cells was evaluated with standard current-voltage and incident-photon-to-collected-electron efficiency measurements, and physical parameters of the devices were characterised with frequency- and time-resolved techniques such as electrochemical impedance spectroscopy, intensity-modulated photovoltage/photocurrent spectroscopy, and open circuit voltage decay measurements, respectively. Overall, the work highlights the importance of surface passivation of QDs, loading of the QDs onto porous semiconducting oxide electrodes, as well as the significance of interfacial effects between QDs, oxides and hole transporter to achieve high-efficiency devices

FABRICATION OF FLEXIBLE QUASI-INTERDIGITATED BACK-CONTACT PEROVSKITE SOLAR CELLS

Perovskites are a promising class of semiconductor materials, which are being studied intensively for their applications in emerging new flexible optoelectronic devices. In this paper, device manufacturing and characterization of quasi-interdigitated back-contact perovskite solar cells fabricated on flexible substrates are studied. The photovoltaic parameters of the prepared flexible quasi-interdigitated back-contact perovskite solar cells (FQIBC PSCs) are obtained for the front- and rear-side illumination options. The dependences of the device’s open-circuit potential and short-circuit current on the illumination intensity are investigated to determine the main recombination pathways in the devices. Spectral response analysis of the devices demonstrates that the optical transmission losses can be minimized when FQIBC PSCs are illuminated from the front-side. Optoelectronic simulations are used to rationalize the experimental results. It is determined that the obtained FQIBC PSCs have high surface recombination losses, which hinder the device performance. The findings demonstrate a process for the fabrication of flexible back-contact PSCs and provide some directions for device performance improvements

SELF-POWERED ORGANOMETAL HALIDE PEROVSKITE PHOTODETECTOR WITH EMBEDDED SILVER NANOWIRES

Metal–semiconductor–metal (MSM) configuration of perovskite photodetectors (PPDs) suggests easy and low-cost manufacturing. However, the basic structures of MSM PPDs include vertical and lateral configurations, which require the use of expensive materials such as transparent conductive oxides or/and sophisticated fabrication techniques such as lithography. Integrating metallic nanowire-based electrodes into the perovskite photo-absorber layer to form one-half of the MSM PPD structure could potentially resolve the key issues of both configurations. Here, a manufacturing of solution-processed and self-powered MSM PPDs with embedded silver nanowire electrodes is demonstrated. The embedding of silver nanowire electrode into the perovskite layer is achieved by treating the silver nanowire/perovskite double layer with a methylamine gas vapor. The evaporated gold layer is used as the second electrode to form MSM PPDs. The prepared MSM PPDs show a photoresponsivity of 4 105 AW1 in the UV region and 2 105 AW1 in the visible region. On average, the devices exhibit a photocurrent of 1.1 106 A under white light (75 mW cm2) illumination with an ON/OFF ratio of 83.4. The results presented in this work open up a new method for development and fabrication of simple, solution-processable MSM self-powered PPDs

Dipole-field-assisted charge extraction in metal-perovskite-metal back-contact solar cells

Hybrid organic-inorganic halide perovskites are low-cost solution-processable solar cell materials with photovoltaic properties that rival those of crystalline silicon. The perovskite films are typically sandwiched between thin layers of hole and electron transport materials, which efficiently extract photogenerated charges. This affords high-energy conversion efficiencies but results in significant performance and fabrication challenges. Herein we present a simple charge transport layer-free perovskite solar cell (PSC), comprising only a perovskite layer with two interdigitated gold back-contacts. Charge extraction is achieved via self-assembled molecular monolayers (SAMs) and their associated dipole fields at the metal/perovskite interface. Photovoltages of approximately 600 mV generated by SAM-modified PSCs are equivalent to the built-in potential generated by individual dipole layers. Efficient charge extraction results in photocurrents of up to 12.1 mA/cm2 under simulated sunlight, despite a large electrode spacing.Comment: 18 pages, 5 figure

Cellulose Nanocrystal-Templated Tin Dioxide Thin Films for Gas Sensing.

Porous tin dioxide is an important low-cost semiconductor applied in electronics, gas sensors, and biosensors. Here, we present a versatile template-assisted synthesis of nanostructured tin dioxide thin films using cellulose nanocrystals (CNCs). We demonstrate that the structural features of CNC-templated tin dioxide films strongly depend on the precursor composition. The precursor properties were studied by using low-temperature nuclear magnetic resonance spectroscopy of tin tetrachloride in solution. We demonstrate that it is possible to optimize the precursor conditions to obtain homogeneous precursor mixtures and therefore highly porous thin films with pore dimensions in the range of 10-20 nm (ABET = 46-64 m2 g-1, measured on powder). Finally, by exploiting the high surface area of the material, we developed a resistive gas sensor based on CNC-templated tin dioxide. The sensor shows high sensitivity to carbon monoxide (CO) in ppm concentrations and low cross-sensitivity to humidity. Most importantly, the sensing kinetics are remarkably fast; both the response to the analyte gas and the signal decay after gas exposure occur within a few seconds, faster than in standard SnO2-based CO sensors. This is attributed to the high gas accessibility of the very thin porous film

Dynamic Chemical Passivation of Absorber Layer Trap States and its Real-time Effect on the Device Performance in Back-Contact Perovskite Solar Cells

Hybrid organic-inorganic perovskites have been identified as one of the most promising classes of materials for photovoltaic and optoelectronic applications, due to their excellent electronic and optical properties, combined with their ease of fabrication. The efficiency of perovskite solar cells (PSCs) has increased at a remarkably fast pace, with the current maximum certified power conversion efficiency (PCE) reaching 25.2%. Conventional solid-state hybrid organic-inorganic perovskite-based solar cells have a sandwich type structure in which the perovskite absorber layer is positioned between bottom and top electrodes, typically a transparent conducting oxide (TCO) layer on glass, and an evaporated thin layer of gold or silver, respectively. Such an architecture for PCSs allows illumination of the cells only from the TCO side. Alternatively, the back-contact architecture offers the possibility of positioning both electrodes on one side of the absorber layer and shining light directly on the photoactive layer [1, 2]. This helps to avoid the occurrence of transmission losses caused by the charge collecting TCO electrode in the conventional sandwich structure for PSCs, and may have some potential application in constructing four or two terminal tandem solar cell devices. The back-contacted device architecture is also useful for conducting fundamental studies as it has an exposed photoactive area, permitting in situ measurements on the effects of chemical treatment, passivation and annealing. I will present a successful application of back-contact PSCs in studying the dynamic effect of a chemical passivation of the perovskite absorber layer and it is real-time influence on the device performance

Back-contact perovskite light-emitting diodes

Light-emitting diodes utilizing halide perovskites have experienced rapid advancements in recent years, demonstrating notable external quantum efficiencies. Despite these strides, the practical implementation of such devices remains constrained. In this contribution, we are dedicated to developing perovskite light-emitting diodes with a back-contact architecture using the MAPbBr3 active layer and SnO2 and Ni/NiOx back electrodes. The quantum efficiency of the fabricated devices stands at 0.015%. The operational voltage of the light-emitting diodes is characterized by its pronounced low values, attaining a maximum luminance of 70 cd/m2 at a mere 3.2 V. These results demonstrate the considerable promise of the developed back-contact perovskite light-emitting diodes for prospective applications in advanced display technologies and light communication systems

THE EFFECTS OF DIFFERENT ELECTRON TRANSPORT LAYER MATERIALS ON THE PHOTOVOLTAIC PROPERTIES OF FLEXIBLE AND PRINTED PEROVSKITE SOLAR CELLS

This work is dedicated to fabricate PSCs on the surface of flexible polyethylene terephthalate with a layer of transparent conducting indium-tin-oxide (PET/ITO) using a slot-die coating method and studying the effect of different electron-transporting layers materials on the performance of FPSCs